1. Field of the Invention
This invention relates to a fuel injection control system for internal combustion engines, for controlling the amount of fuel injected into the intake pipe of the engine and the timing of injection of the fuel.
2. Prior Art
Conventionally, a fuel injection control system of this kind has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 63-129141, in which, to overcome the inconvenience of an insufficient fuel supply which is liable to occur when load on an internal combustion engine drastically increases, e.g. during acceleration of the engine the timing of fuel injection is set for each combustion cycle such that fuel is injected over two different time periods, i.e. a first injection time period well in advance of the intake stroke, and a second injection time period closer to the intake stroke, whereby the whole amount of fuel calculated for the combustion cycle is injected over the first injection time period, and if required, an additional amount of fuel supply calculated for a shortage in the fuel amount due to a change in load on the engine detected over a time interval between the two injection time periods is injected over the second injection time period for replenishment of the fuel supply.
Further, another kind of fuel injection control system adapted to perform split injection for a cylinder so as to avoid an overlapping time period during which an intake valve and an exhaust valve concurrently open for the cylinder has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 52-31223, in which if the start of a first fuel injection is delayed due to a sudden change in operating conditions of the engine, a second fuel injection is carried out to inject an amount of fuel which should have been injected in the first fuel injection, depending on the operating conditions of the engine and the delay of the start of the first fuel injection, or alternatively the termination of the first fuel injection is retarded by a time period corresponding to the delay of the start of the first fuel injection.
However, according to the former proposed control system, even if it is determined during the first injection time period that the fuel injection amount should be increased, the short amount of fuel supply is not actually replenished until the second fuel injection, which results in still insufficient controllability of the air-fuel ratio of a mixture supplied to the engine. Further, this prior art does not contemplate cases in which the amount of fuel injection is required to be decreased due to a change in the operating conditions of the engine, which prevents improvement in the controllability of the engine upon a sudden decrease in load on the engine.
Further, the fuel injection control by the latter proposed control system compensates for a delay in the start of fuel injection, but does not correct the amount of fuel injection per se, which also leaves room for improvement in the controllability.